Solenoid actuators of the subject character generally include a ferromagnetic armature mounted for motion through a defined stroke, and a stator positioned adjacent to the armature with a coil for energizing the stator and drawing the armature toward the stator. The armature is coupled to a load, such as a valve element or other control device. The characteristic of force generated by the stator on the armature (and by the armature on the load) versus stroke displacement of the armature varies with a number of design factors or considerations, including geometry of the air gap between the stator and armature. A number of air gap geometries, defined by the opposing surfaces of the armature and stator, have been proposed in the art, including air gaps of at least partially conical construction as in U.S. Pat. Nos. 3,312,842 and 4,583,067.
A general object of the present invention is to provide improvements in construction of solenoid actuators of the subject character that achieve improved efficiency in terms of reduced size and cost for a given output power or stroke requirement. Another and more specific object of the present invention is to provide a solenoid actuator that is characterized by increased output force, as compared with prior art constructions, in the initial portion of the armature stroke, which helps overcome inertia at the load coupled to the armature. Another specific object of the present invention is to provide a solenoid actuator of the described character that is adapted to generate increased force for a given stroke displacement, as compared with prior art devices of a similar character, while operating at or above the point of electromagnetic saturation of the armature and stator structures.